Pulse-Width-Modulation (PWM) mode, compared to Pulse-Frequency-Modulation (PFM) mode, has poor conversion efficiency at low loads due to the constant switching frequency. At low loads (i.e., loads consuming less current), voltage regulators (VRs) may use PFM mode instead of PWM mode. Typically, VRs operating in PWM mode operate at low frequencies e.g., 1 MHz. Low frequency operation is possible because of off-die inductors which are large in size. Such large inductors are not suitable for use in today's mobile devices (e.g., smart devices, tablets, smart phones, etc.) which have small form factor compared to desktop computers, for example.
However, when inductors are placed on-die (e.g., in microprocessors) for voltage regulation, inductor size is reduced because increasing die size to accommodate a large inductor size increases manufacturing costs of the die. A VR with smaller sized inductor can operate with comparable efficiency as a VR with large sized inductor by increasing switching frequency of the VR using smaller sized inductor. For example, switching frequency can be increased to 100 MHz (instead of typical low frequency of 1 MHz). However, by increasing switching frequency (e.g., from 1 MHz to 100 MHz) to improve VR efficiency, power consumption increases.